Pancreatic functioning will be examined in recipients of pancreas-kidney and kidney transplants as well as non-diabetic healthy subjects. Subjects will undergo 3 treatments; bolus injection of C-peptide, oral glucose ingestion and isoglycemic intravenous glucose tolerance test. The bolus injection of C-peptide enabled us to determine each individual's C-peptide clearance kinetics which were then applied to a mathematical model to determine absolute insulin secretion in each individual following the oral and intravenous glucose challenges.